European patent document EP 1 707 692 A1 discloses a telescoping water outlet of this general type, which has an outflow conduit system that can be telescoped by a displacement distance. The outflow conduit system of this prior-art water outlet comprises a through-flow pipe, which is retained on the basic fitting body, and an outflow pipe, which can be moved longitudinally in relation to the through-flow pipe, one pipe being an inner pipe and the other being an outer pipe. The inner pipe has a closed end and a radial through-passage at a distance from the closed pipe end, which distance corresponds at least to the displacement distance. The radial through-passage connects an interior of the inner pipe permanently to a casing space, which has a constant volume, and is delimited by the inner pipe and the outer pipe.
Since the casing space, through which the water flows, maintains a constant volume when the telescoping water outlet is extended or retracted (when the control cartridge disposed in the basic fitting body is closed) no water flows out of a water-outflow opening of the sanitary fitting when the system is retracted, and no air, water or solid is taken into the outflow conduit system through the water-outflow opening when the system is extended. However, the maximum possible extension length of this prior-art telescoping water outlet is always less than half the overall length of its telescoped outflow conduit system.
The outflow conduit system of this prior-art water outlet is free from the action of different hydraulic forces which would be able to displace the outflow pipe. However, an undesirable longitudinal movement of the outflow pipe can occur if the axis of the water outflow direction and the direction of movement of the fitting are parallel and if the outflow pipe consequently retracts at the water outlet. Moreover, the water outlet disclosed in EP 1 707 692 A1 has a complex internal structure producible only with considerable expenditure and relies on a basic fitting body, which has been adapted in terms of design and the flow conditions of which must suit the outflow conduit system. Since this prior-art water outlet thus cannot be mounted subsequently on an already existing fitting, the possible applications for the water outlet disclosed in EP 1 707 692 A1 are further limited.